There is known a fixing device including an infrared heater, a nip plate that is heated by the infrared heater, a cylindrical fusing belt, and a pressure roller that pinches the fusing belt between the pressure roller and the nip plate. In this fixing device, the fusing belt rotates by rotation of the pressure roller. A toner image on a sheet is thermally fixed to the sheet when the sheet is conveyed between the pressure roller and the fusing belt. In recent years, the nip plate is formed by rolling with a pair of reduction rolls. In this case, very small protrusions and depressions of the reduction rolls are transferred on surfaces of the nip plate. Hence, a plurality of lines, i.e., roll marks, are formed.
If the nip plate is arranged such that the roll marks are orthogonal to a sheet conveying direction, sliding resistance of the fusing belt with respect to the nip plate increases and the fusing belt may not properly rotate. To improve sliding performance, a lubricant may be applied between the fusing belt and the nip plate. In this case, however, the lubricant is excessively held by the roll marks that are orthogonal to the conveying direction. The sliding resistance of the fusing belt with respect to the nip plate may increase in an area located downstream of the position where the lubricant is held.